A disk drive or direct access storage device ("DASD") includes several disks which look similar to records used on a record player or compact disks which are used in a CD player. The disks are stacked on a spindle, much like several 45 rpm records awaiting to be played. In a disk drive, however, the disks are mounted to the spindle and spaced apart so that the separate disks do not touch each other.
The surface of each disk is uniform in appearance. However, in actuality, the surface of each disk is divided into portions where data is stored. There are a number of tracks of the disk situated in concentric circles like rings on a tree. Compact disks have tracks as do the disks in a disk drive. The tracks in either the disk drive or the compact disk essentially replace the grooves on a conventional record. Each track in a disk drive is further subdivided into a number of sectors, where each sector is essentially just one section of the circumferential track.
Disks in a disk drive are made of a variety of materials. High capacity magnetic disks use a thin film magnetic media plated or vacuum deposited upon a substrate. Protective and lubricating layers may be applied over the magnetic active layer. Most commonly, the substrate of the disk is made of metal, plastic, or glass material. The material from which the disk is made determines how data is stored on the disk. A plastic disk, such as those used as CDs, stores data using lasers and a laser is used to read the data back. Storage of data on a metal disk entails magnetizing portions of the disk in a pattern which reflects the data.
To store data on a magnetic disk with a glass or metal substrate, the disk is magnetized. In order to magnetize the surface of a disk, a small ceramic slider which contains a magnetic transducer known as a write head is passed over the surface of the disk. More specifically, the write head is flown at a height of less than six millionths of an inch from the surface of the disk and is flown over the track as the write head is energized to various states causing the track below to be magnetized to represent the data to be stored.
To retrieve data stored on a magnetic disk, a ceramic slider which contains a read head is flown over the metal disk. The magnetized portions of the disk induce a current in the read head. By looking at output from the read head, the data can be reconstructed for use by the computer system. Typically, the same ceramic slider contains both a read head and a write head.
A smooth, specular recording surface is thus preferred, as well as a smooth opposing surface of the associated transducing head. This permits closer proximity of the head to the disk, and more predictable and consistent behavior of the air bearing supporting the head. However, if the head surface and recording surface are too flat, the precision match of these surfaces give rise to excessive stiction and friction during the start up and stopping of the disk, causing wear to the head and recording surface which eventually can lead to a head crash. In recognition of this difficulty, the recording surfaces of magnetic disks often are intentionally roughened, known as textured, to reduce the head/disk friction.
The topography of the surface of the disk has important effects on performance. Texturing or polishing the surface with a generally circumferential pattern improves the magnetic performance and increases the potential data density by improving the squareness and orientation ratio of the magnetic active layer. Providing texture in the landing zone has the three benefits of reducing stiction and friction, enhancing lubrication and reducing wear. Increasing the surface roughness reduces the problems that arise from adhesion of the head to the static disk surface.
Several methods exist in the art for texturing a disk. U.S. Pat. No. 5,482,497 to Gonnella, et al., discloses using an abrasive slurry to texture disks. Other examples of texturing methods are discussed in Gonnella at col. 2, lines 29-40.
The present invention pertains to the use of lasers to texture magnetic disks. More generally, the invention pertains to the use of lasers to texture glass or glass-containing substrates, such as a glass disk.